Dual chamber gas exchanger and method of use for respiratory support

ABSTRACT

The device of the present invention includes a dual chamber gas exchanger that is configured for increased flexibility and scalability for many clinical applications. The dual chamber oxygenator can be configured and used in various applications, such as in a heart-lung machine for cardiopulmonary support during cardiothoracic surgery, in an extracorporeal membrane oxygenation (ECMO) circuitry, as a respiratory assist device for patients with lung failure, and the like. The dual chamber gas exchanger features two sweep gas flow paths and two gas exchange membrane bundles enclosed in a housing structure with various blood flow distribution and gas distribution mechanisms. The gas exchanger includes an outer housing, an intermediate housing, two gas exchange fiber bundles, a blood inlet, a blood outlet, two gas inlets, two gas outlets, two gas distribution chambers and an optional heat exchanger.

CROSS-REFERENCES TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.16/791,117, filed on Feb. 14, 2020, which is a continuation ofinternational patent application PCT/US2018/000133, filed on Aug. 15,2018, which claims the benefit of provisional patent application62/545,512, filed on Aug. 15, 2017, the full disclosure of which isincorporated herein by reference.

STATEMENT ON GOVERNMENT INTEREST

This invention was made with government support under Grant NumberHL118372 awarded by the National Institutes of Health. The governmenthas certain rights in the invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates generally to medical devices and methods.More particularly, the present invention relates to devices forextracorporeal membrane oxygenation, respiratory support, andcardiopulmonary support.

Oxygenating blood with artificial devices began in the 1930s. Earlyblood oxygenators, such as thin film blood oxygenators and bubbleoxygenators, were based on exposing blood directly to oxygen or air.Direct contact of blood with oxygen is an effective way of exchanginggases, but it also damages the blood's proteins and formed elements.Thus, these earlier blood oxygenators could only be used for limitedtime, such as for a few hours.

Other approaches, such as gas-permeable solid membranes, separated theblood from sweep gas to eliminate damage caused by direct blood and gascontact. Solid membranes were the basis for many design platforms, butwere hindered by manufacturing challenges and thrombogenicity. Thus,hollow fiber membranes emerged. Hollow fiber membranes enabled thedesign and construction of efficient and small blood oxygenators withlow prime volume, increased ratio of gas-exchange surface area to bloodvolume, and reduced thrombogenicity. Many current blood oxygenatorsinclude hollow fibers of microporous materials.

Many types of blood oxygenators based on hollow fiber membrane materialshave been designed and developed. Oxygenators with hollow fibermembranes typically include a single chamber with one fiber bundle andare characterized by the blood flow path within the fiber bundles. Forexample, four types of blood flow paths are (1) longitudinal (axial)flow through an annular bundle; (2) circumferential flow around anannular bundle; (3) transverse flow across a bundle of substantiallyrectangular cross-section; and (4) radial flow through an annularbundle.

Although the membrane blood oxygenators based on the above principlesare generally acceptable for cardiopulmonary bypass during open-heartsurgeries, they have a number of problems when they are used forrespiratory support over longer durations (days to weeks). For example,typical hollow fiber membrane blood oxygenators have relatively largeblood-contacting surface areas, large prime volume, large physical sizeswith very limited long-term biocompatibility and durability, and limitedflexibility for various clinical applications. Patients on respiratorysupport with these current blood oxygenators are often bedridden withlimited mobility due to complexity and bulky size of the typical bloodoxygenators caused by the inherent blood fluid dynamics. Furthercomplications are caused by non-uniform blood flow through the fibermembranes and laminar boundary flow zones between blood cells and fibermembranes.

Non-uniform blood distribution can cause many problems in hollow fibermembrane blood oxygenators, such as hyper- and hypo-perfusion of theblood in the flow path. Hyper-perfusion does not have any additionalbenefits relative to oxygen-saturated blood. However, hypo-perfusion canbe detrimental to the patient. Hollow fiber membrane blood oxygenatorsuse long flow paths to increase the blood contact with the larger fibermembrane surface area to ensure that all blood cells in hypo-perfusionregions are well-oxygenated. However, large gas exchange membranesurface areas and large prime volume provide poor biocompatibility andwearability. Non-uniform blood flow can also induce excessive mechanicalshear stresses or stasis in the blood flow path in oxygenators. Theseare the major contributing factors to blood activation and thrombosisformation, resulting in limited long-term biocompatibility anddurability.

In addition to these technical issues, typical hollow fiber membraneblood oxygenators lack flexibility for various clinical applications.Often, one device only serves for one application, which may beinsufficient for some patients. These oxygenators often have limitedcapability for removing carbon dioxide while transferring oxygen to somepatients. Moreover, high sweep gas flow rates are required to removecarbon dioxide, or blood flow rates must remain low because of limitedsweep gas flow rates (e.g., in ambulatory use). Low blood flow rates canresult in thrombosis forming inside oxygenators.

In various clinical applications, such as in a hospital, ambulatory, orhome setting, the requirement for and availability of the sweep gas canvary. In particular, oxygen sources can be a challenge in ambulatoryapplications, such as when a bulky oxygen tank or a large heavy oxygenconcentrator is required. Thus, typical blood oxygenators can limitpatient mobility and flexibility.

Removing carbon dioxide from the oxygenator typically requires higherflow rates and a gas that is nearly free of carbon dioxide. Oxygen is atypical primary sweep gas to deliver oxygen and remove carbon dioxide.For example, at a sweep gas flow rate of 1:1 to blood flow rate, only 5%(50 cc/liter) of the oxygen is delivered to the circulating blood.However, increasing carbon dioxide removal requires the sweep gas toblood flow rate ratio above 1:1. Thus, the percentage of oxygenutilization is much less than 5% and the efficiency of oxygen deliveryis extremely poor and costly. Even in an acute setting at 5 liters/minover a 24-hour period a patient would consume 7,200 liters of oxygenwith less than 5% being delivered to the patient. Room air at high flowrates can also be a sufficient sweep gas to remove carbon dioxide.Current oxygenators have limited adjustability and therefore lackprecise control of oxygen delivery and carbon dioxide removal.

Thus, it can be seen that there is a need for improved oxygenators thatefficiently use sweep gases for gas exchange. Such an oxygenator canserve various applications and patients.

2. Background of the Invention

Relevant background patents include: US Patent Publ. No. 2013/0296633;U.S. Pat. Nos. 9,320,844; 8,709,343; 8,529,834; 7,871,566; 5,270,005;8,795,220; 8,545,754; 8,518,259; and 6,998,093.

BRIEF SUMMARY OF THE INVENTION

The device of the present invention includes a gas exchanger that isconfigured for increased flexibility and scalability for many clinicalapplications. The gas exchanger can be configured and used in variousapplications, such as in a heart-lung machine for cardiopulmonarysupport during cardiothoracic surgery, in an extracorporeal membraneoxygenation (ECMO) circuitry, as a respiratory assist device forpatients with lung failure, and the like. In some embodiments, the dualchamber gas exchanger features two sweep gas flow paths. In otherembodiments, two gas exchange membrane bundles are enclosed in a housingstructure that provides two chambers that isolate the gas flow andprovide for sequential blood flow with various blood flow distributionand gas distribution mechanisms. In some embodiments, the gas exchangerincludes an outer housing, an intermediate housing, two gas exchangefiber bundles, a blood inlet, a blood outlet, two gas inlets, two gasexhausts or outlets, two gas distribution chambers and an optional heatexchanger. In particular embodiments, the gas exchanger may beconfigured to manipulate the concentration of the sweep gas that isexposed to the patient's blood to transfer oxygen and to remove thecarbon dioxide, such as by using sweep gases that include oxygen,blended oxygen and atmospheric air, other medical gases, and the like.

The present invention includes a compact dual chamber gas exchangerhaving a low priming volume, small gas exchange surface area, and theability to disrupt boundary layer effect. The dual chamber gas exchangeralso removes carbon dioxide while providing oxygen transfer. The dualchamber gas exchanger includes an outer housing that encloses theinternal components and hosts connectors, a blood inlet, and an annularouter fiber bundle of hollow fiber membranes. The dual chamber gasexchanger is configured for a wide range of uses, such ascardiopulmonary bypass, extracorporeal membrane oxygenation (ECMO), asan integrated pump-oxygenator, passive respiratory support device (e.g.,configuration for right ventricle to pulmonary artery or configurationfor pulmonary artery to left atrium), ambulatory cardiopulmonary, andrespiratory support, or the like.

The outer fiber bundle is centrally located in the housing and furtherincludes fibers, upper potting, and lower potting. The upper potting andlower potting hold the fibers within the housing. In one embodiment, theouter fiber bundle includes a blood distributor configured as a spiralvolute wrapping around the inner surface of the housing. The blooddistributor is coupled to the blood inlet near the upper potting orlower potting. The blood distributor is configured to discharge bloodaround the outer fiber bundle such that it creates a pressurized annularblood volume surrounding the outer fiber bundle, and such that bloodflows axially through the gas exchange membranes of the outer fiberbundle.

In an alternative embodiment, the blood distributor of the dual chambergas exchanger includes a rectangular inlet or first gate opening at oneside of the outer housing from one end to the other end of the pottingareas. The rectangular gate opening is typically a vertically orientedslot configured to couple the blood inlet to discharge the incomingblood to the outer fiber bundle. Thus, the blood generally flowscircumferentially through the gas exchange membranes of the outer fiberbundle, usually exiting at a second or outlet gate as describedhereinbelow.

One embodiment of the dual chamber gas exchanger further includes anannular inner fiber bundle of hollow fiber membranes. The annular innerfiber bundle is concentrically located within the outer fiber bundle,and further includes fibers, an upper potting, and a lower potting. Theupper potting and lower potting of the annular inner fiber bundle holdthe fibers in place in the housing.

Another embodiment of the dual chamber gas exchanger further includes anintermediate housing, typically formed as a cylindrical wall, that isconfigured to substantially separate the outer fiber bundle and innerfiber bundle. Thus, the intermediate housing is generally locatedbetween a radially inward surface of the outer fiber bundle and aradially outward surface of the inner fiber bundle. An intermediateannular space is formed between a radially inward surface of theintermediate housing and the radially outward surface of the inner fiberbundle which provides an annular flow path around the inner fiber bundleto allow a radially inward blood flow path through the inner fiberbundle. In other embodiments, the intermediate housing may be configuredto provide circumferential or axial flow through the inner fiber bundle.

The dual chamber gas exchanger further includes a thin slot at the upperpotting area, which allows the blood to exit the outer fiber bundle andenter the intermediate annular space existing between the intermediatehousing wall and the outer annular surface of the inner fiber bundle. Inanother embodiment having a circumferential flow path through the outerfiber bundle, the dual chamber gas exchanger includes a rectangular gatethat is configured to allow blood flow to flow from the outer fiberbundle into the intermediate annular space.

The dual chamber gas exchanger includes components for transferringfluids, including a blood inlet, a blood outlet, and at least one gasinlet. The blood outlet is configured to collect the oxygenated bloodfrom the fibers and further couples to a cannula through which theoxygenated blood is returned to the patient. The blood outlet isgenerally located at a central location at a top portion of the housingand is fluidly coupled to the inner fiber bundle, such as to the upperpotting of the inner fiber bundle.

The at least one gas inlet, such as two gas inlets of one embodiment,are configured to provide separate gas passages for gases, such asoxygen and/or air, to enter the hollow fibers. The at least one gasinlet is positioned on a bottom portion of the housing. In oneembodiment, the at least one gas inlet forms two separate gas chamberswith the lower potting of the two bundles of hollow fiber membranes.

The two gas outlets are configured to provide gas passages for gases,such as the oxygen and /or air to leave the hollow fibers. The gasoutlets are generally located on the top portion of the housing andgenerally form two separate gas chambers with the upper potting of thetwo bundles of hollow fiber membranes.

In another embodiment, the blood gas exchanger includes a blood sampleport or a blood gas sensor that is configured to allow external samplingof the blood within the blood gas exchanger. For example, the bloodsample port may be fluidly coupled to the blood inlet or blood outlet.The blood sample port may further include an oxygen saturation detectoraffixed to the blood outlet, and a temperature port affixed to the bloodoutlet.

While there may be different considerations and requirements for eachclinical scenario, a blood exchanger that is efficient, long-termbiocompatible, long-term durable and versatile is universally desirable.In other words, it is desirable to use minimal necessary fiber membranesto achieve the most efficient gas transfer while minimizing blood traumaand maintaining long-term durability and reliability. It is alsoflexible to accommodate various sweep gas sources to provide oxygentransfer, carbon dioxide removal, or both, for various clinicalapplications.

In a first aspect, the present invention provides a blood oxygenatorcomprising a housing which includes a blood inlet, a blood outlet, astripping gas inlet, an oxygenation gas inlet, and at least one gasoutlet. An oxygenator fiber bundle is disposed within the housing and isconfigured so that blood flows through a blood flow region in theoxygenator fiber bundle in a predetermined path from the blood inlet tothe blood outlet. The stripping gas inlet is configured to direct a flowof stripping gas through a stripping region of the oxygenator fiberbundle to the at least one gas outlet. The oxygenation gas inlet isconfigured to direct a flow of oxygenation gas through an oxygenationregion of the oxygenator fiber bundle to the at least one gas outlet.The stripping gas region of the oxygenator fiber bundle is upstream ofthe oxygenation region of the oxygenator fiber bundle. The term“upstream” refers to the direction of blood flow so that the blood to beoxygenated is first exposed to the stripping gas in the stripping regionand thereafter exposed to the oxygenation gas in the oxygenation regionof the fiber bundle.

In a first set of exemplary embodiments, the blood oxygenators of thepresent invention may have a cylindrical fiber bundle where at least aportion of the blood flow path is in a radially inward or radiallyoutward direction. In such embodiments, a portion of the fiber bundlealong a central axis will typically be open to provide an outlet orinlet plenum to receive blood from or distribute blood to thecylindrical fiber bundle, respectively. In still other embodiments, thefiber bundle is cylindrical and at least a portion of the blood flowpath follows an annular path, where the bundle will typically have ablood inlet or outlet plenum along the central axis of the fiber bundle.In still other embodiments, at least a portion of the blood flow pathmay be unidirectional across the oxygenator fiber bundle.

In certain specific examples, the fiber bundle of the oxygenator iscylindrical, having an outer portion of the blood flow path whichfollows an annular path and an inner portion of the blood flow pathwhich follows a radially inward path. In these examples, the blood inlettypically feeds the outer portion of the fiber bundle, and the innerportion of the fiber bundle feeds the blood outlet. More specifically,the stripping region may be disposed at least in part in the outerportion of the blood flow path and the oxygenation region may bedisposed at least in part in the inner portion of the blood flow pathwhere the blood inlet feeds the inner portion and the outer portionfeeds the blood outlet. Alternatively, the stripping region may bedisposed at least in part in the inner portion of the blood flow pathand the oxygenation region is disposed at least in part in the outerportion of the blood flow path.

The blood oxygenator may further comprise a cylindrical wall separatingthe outer portion and the inner portion of the cylindrical fiber bundle,where blood flows from the blood inlet through an axial opening in thehousing into the outer portion of the fiber bundle and flows annularlythrough the outer portion of the fiber bundle to thereafter through anaxial opening in the cylindrical wall and into a distribution ringsurrounding the inner bundle from where the blood flows radiallyinwardly through the inner portion of the fiber bundle to an axialcollection region along a center axis of the inner portion of the fiberbundle.

In other embodiments, the oxygenation fiber bundles of the bloodoxygenator of the present invention may have a cross-sectional areawhere the stripping region that receives the stripping gas from thestripping gas inlet has an inlet area that comprises from 20% to 80% ofsaid cross-sectional area and the oxygenation region that receives theoxygenation gas from the oxygenation gas inlet has an inlet area thatcomprises from 80% to 20% of said cross-sectional area.

In still further embodiments, the blood oxygenators may further comprisea manifold divider which divides and directs both (1) the stripping gasfrom the stripping gas inlet to the stripping region of the oxygenatorfiber bundle and (2) the oxygenation gas from the oxygenation gas inletto the oxygenation region of the oxygenator fiber bundle. The manifolddivider may be disposed in a manifold which receives the stripping gasfrom the stripping gas inlet and the oxygenation gas from theoxygenation gas inlet, where the manifold is typically open to an entiregas inlet side of the oxygenation fiber bundle and placement of themanifold divider controls an inlet area of the stripping region thatreceives the stripping gas from the stripping gas inlet and an inletarea of the oxygenation region that receives the oxygenation gas fromthe oxygenation gas inlet. The manifold divider may be fixed or may bemoveable, the latter case allowing the relative areas of the strippingand oxygenation regions in the fiber bundle to be adjusted during use orbetween uses.

In yet further embodiments, the oxygenation fiber bundles of the bloodoxygenators may comprise an upper potting and a lower potting. Themanifold may be located within the housing adjacent to one of thepottings, and a blood pump may be connected to said blood inlet. Anoxygenation gas source may be connected to the oxygenation gas inlet anda stripping gas source may be connected to the stripping gas inlet.

In a second aspect, the present invention provides methods foroxygenating blood. A blood oxygenator having a (1) housing with a bloodinlet, a blood outlet, a stripping gas inlet, an oxygenation gas inlet,and at least one gas outlet and (2) an oxygenator fiber bundle disposedwithin the housing is provided. Blood is flowed through the blood inlet,through the oxygenator fiber bundle, and out the blood outlet. Astripping gas is flowed through the stripping gas inlet, and anoxygenation gas is flowed through the oxygenation gas inlet. Thestripping gas flows through a stripping region of the oxygenator fiberbundle to the at least one gas outlet, and the oxygenation gas flowsthrough an oxygenation region of the oxygenator fiber bundle to the atleast one gas outlet. The stripping gas region of the oxygenator fiberbundle is disposed upstream of the oxygenation region of the oxygenatorfiber bundle. The arrangement achieves a particularly efficient CO₂removal and oxygen incorporation and, in particular, can reduce the needfor pure oxygen to perform both the CO₂ stripping and the bloodoxygenation.

In particular embodiments of the methods of the present invention, theblood may travel through the stripping region of the oxygenator fiberbundle in an annular flow path, and in other embodiments, the bloodtravels through the oxygenation region of the oxygenator fiber bundle ina radially inward flow path. In still other embodiments, the blood maytravel through the stripping region and the oxygenation region of theoxygenator fiber bundle in a straight direction. In some instances, theblood may travel through the oxygenator fiber bundle in a substantiallyuniform blood flow distribution. In other instances, the fiber bundlemay have a cross-sectional area where the stripping region that receivesthe stripping gas from the stripping gas inlet has an inlet area thatcomprises from 20% to 80% of the cross-sectional area and theoxygenation region that receives the oxygenation gas from theoxygenation gas inlet has an inlet area that comprises from 80% to 20%of the cross-sectional area. The methods of the present invention mayfurther comprise moving a manifold divider which directs the flowstripping gas from the stripping gas inlet to the stripping region ofthe oxygenator fiber bundle, as well as the oxygenation gas from theoxygenation gas inlet to the oxygenation region of the oxygenator fiberbundle, in order to adjust relative areas of the stripping region andthe oxygenation region of the oxygenation fiber bundle.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: Perspective view of a first embodiment of a dual chamber gasexchanger with a circumferential-radial flow path, according to theprinciples of the present invention.

FIG. 2: Vertical cross-sectional view of the dual chamber gas exchangerof FIG. 1 having a circumferential flow path design in an outer fiberbundle and a radial flow path in an inner fiber bundle, two gas inlets,and two gas exhausts.

FIG. 3: Vertical cross-sectional view of the dual chamber gas exchangerof FIGS. 1 and 2 illustrating blood flow paths in a blood distributorand the inner fiber bundle and the outer fiber bundle.

FIG. 4: Horizontal cross-sectional view of the dual chamber gasexchanger of FIGS. 1-3 illustrating a circumferential blood flow path inthe outer fiber bundle starting from the distributor through Gate 1 tothe outer fiber bundle and through Gate 2 to the inner fiber bundle.

FIG. 5: Perspective view of a dual chamber gas exchanger with anaxial-radial flow path, according to another embodiment of the presentinvention.

FIG. 6: Vertical cross-sectional view of the dual chamber gas exchangerof FIG. 5 with an axial flow path design in an outer fiber bundle and aradial flow path in an inner fiber bundle, two gas inlets, and two gasexhausts.

FIG. 7: Vertical cross-sectional view of the dual chamber gas exchangerof FIG. 5 illustrating blood flow paths.

FIG. 8A is a top cross-sectional view of the dual chamber gas exchangerof FIG. 5 illustrating a spiral volute having blood flow through Gate 1.

FIG. 8B is a perspective cut-away view of the dual chamber gas exchangerof FIG. 5 illustrating an axial blood flow path through Gate 1 and Gate2 into the inner fiber bundle and exiting the dual chamber gasexchanger.

FIG, 9A is an illustration of a horizontal cross-sectional view ofcomputational fluid dynamics modelling of a blood flow field in the dualchamber gas exchanger embodiment of FIG. 1 at 6 liters per minute.

FIG. 9B is an illustration of a vertical cross-sectional view ofcomputational fluid dynamics modelling of a blood flow field in the dualchamber gas exchanger embodiment of FIG. 5 at 6 liters per minute).

FIG. 10A is an illustration of a horizontal cross-sectional view ofcomputational fluid dynamics modelling of the oxygen transfer processand velocity vectors of the dual chamber gas exchanger embodiment ofFIG. 1 at 6 liters per minute.

FIG. 10B is an illustration of a vertical cross-sectional view ofcomputational fluid dynamics modelling of the oxygen transfer processand velocity vectors in the dual chamber gas exchanger embodiment ofFIG. 5 at 6 liters per minute).

FIG. 11: Schematic of the dual chamber blood oxygenator showing variouscomponents used for a cardiopulmonary bypass surgery application.

FIG. 12: Illustration of a dual chamber gas exchanger for use as adetachable integrated pump-oxygenator (e.g., integratedpump-oxygenator), according to another embodiment of the presentinvention.

FIGS. 13A and 13B: Illustrations of a dual chamber gas exchanger for useas an ambulatory respiratory and/or cardiopulmonary support, accordingto another embodiment of the present invention ((a) harness-likeconfiguration; (b) wheeled configuration).

FIG. 14: Vertical cross-sectional view of a dual chamber gas exchangerwith a radial flow path design in an outer fiber bundle and acircumferential flow path in an inner fiber bundle, according to anotherembodiment of the present invention.

FIG. 15: Vertical cross-sectional view of the dual chamber gas exchangerof the embodiment of FIG. 14 with arrows showing blood flow directions.

FIG. 16: Horizontal cross-sectional view of the blood flow paths in aspiral volute, the outer fiber bundle and the inner fiber bundle of thedual chamber gas exchanger similar to those of FIG. 14.

FIG. 17: Schematic, vertical cross-sectional view of a dual chamber gasexchanger having a radial blood flow through inner and outer annularchambers.

FIG. 18: Vertical cross-sectional view of the dual chamber gas exchangerof the embodiment of FIG. 17 with arrows illustrating radial blood flowpaths in the inner fiber bundle and outer fiber bundles.

FIG. 19: Horizontal cross-sectional view of a spiral volute, the outerfiber bundle, and the inner fiber bundle of the dual chamber gasexchanger illustrating blood flow paths similar to the embodiment ofFIG. 17.

FIG. 20: Vertical cross-sectional view of a dual chamber gas exchangerhaving a radial flow path in an outer fiber bundle and an axial flowpath in an inner fiber bundle, according to another embodiment of thepresent invention.

FIG. 21: Vertical cross-sectional view of the dual chamber gas exchangerof FIG. 20 with arrows illustrating a radial blood flow path in theouter fiber bundle, an axial blood flow path in the inner fiber bundle,two gas inlets, and two gas outlets.

FIG. 22: Horizontal cross-sectional view of a spiral volute blood inletin a dual chamber gas exchanger similar to that of FIG. 20 with arrowsillustrating blood flow paths in the spiral volute and the outer fiberbundle.

FIGS. 23A and 23B: A schematic of alternative gas flow paths in a dualchamber gas exchanger, according to alternative embodiments of thepresent invention, in which an exhausted oxygen-rich sweep gas from oneof an inner fiber bundle or an outer fiber bundle mixes with atmosphericair for use as a sweep gas in the other of the inner fiber bundle orouter fiber bundle (FIG. 23A); and in which each sweep gas is used forthe inner fiber bundle and the outer fiber bundle separately (FIG. 23B).

FIG. 24: Blood flow path and gas flow paths in a dual chamber gasexchanger having a square fiber bundle and two gas inlets, according toanother embodiment of the present invention.

FIG. 25: Blood flow path and gas flow paths in another embodiment of adual chamber gas exchange having regions within the fiber bundle dividedby a moveable wall in a cylindrical gas inlet manifold.

FIG. 26A: Vertical cross-sectional view of a dual chamber gas exchangerwith an alternative partition mechanism.

FIG. 26B: Horizontal cross-sectional view of a variable partitionmechanism similar to that of FIG. 26A with a spiral volute.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1-22, a dual chamber gas exchanger 100 is configuredto use two separate sweep gases (e.g., ventilating gases) to allow thedual chamber gas exchanger 100 to be used in various clinicalapplications. For example, the dual chamber gas exchanger 100 usesseparate flow paths in separate chambers of a dual gas flow chamber 124,such as a first chamber 110 and a second chamber 113, for transferringoxygen to the blood and removing carbon dioxide from the blood. The dualchamber gas exchanger 100 of the current embodiment includes an outerhousing 112, a blood distributor 114, an outer fiber bundle 116 ofhollow membranes, an intermediate housing 118, an inner fiber bundle 120of hollow membranes, an inner flow deflector 122, and the dual gas flowchamber 124. The dual chamber gas exchanger 100 can be used in variousclinical scenarios; for example, cardiopulmonary bypass duringcardiothoracic surgeries, extracorporeal membrane oxygenation (ECMO) forcardiopulmonary support or respiratory support in hospitals, ambulatoryrespiratory support (see FIG. 13) out of intensive care unit, at apatient's home, and the like.

The outer housing 112 and the intermediate housing 118 are configured toenclose the outer fiber bundle 116 to form various blood flow paths inthe outer fiber bundle 116 and the inner fiber bundle 120 (see FIGS. 2,3, 4, 6, 7, 8A,8B, 14, 15, 16, 17, 18, 19, 20, 21, and 22). For example,each of the blood flow paths may be at least one of axial,circumferential, or radial flow paths, etc. The inner flow deflector 122is configured to deflect or guide blood flow from the inner fiber bundle120 towards a blood outlet 144. The inner flow deflector 122 (see FIGS.2, 3, 4, 6, 7, 8B, 14, 15, 17, 18, 20, and 21) of the currentembodiments has a general shape of a cylinder with a conical-like topand is substantially concentrically located in the center of the innerfiber bundle 120.

The dual gas flow chamber 124 receives sweep gas and distributes thesweep gas into the fiber membranes in both the inner fiber bundle 120and the outer fiber bundle 116 (FIGS. 2, 6, 14, 15, 17, 18, 20, 21, and23). The sweep gas of the current embodiments includes air, oxygen, amixture of oxygen and air, or another ventilating gas. The intermediatehousing 118 is configured to allow blood to flow (e.g., in asubstantially radial, axial, and/or circumferential direction) throughthe inner fiber bundle 120, and to enclose the inner fiber bundle 120.The inner fiber bundle 120 and outer fiber bundle 116 includegas-exchange membrane fibers, such as hollow membrane fibers, configuredto transfer oxygen to the blood and remove carbon dioxide from the bloodthat flows across the membrane fibers. The inner fiber bundle 120 andthe outer fiber bundle 116 can be annular fiber bundles (see FIGS. 2, 6,14, 17, 20, and 23A and 23B) or square forms (see FIG. 24) consisting ofa plurality (e.g., thousands) of gas permeable hollow membrane fibers ormembrane fibers. The inner fiber bundle 120 and the outer fiber bundle116 are generally centrally and concentrically located within the outerhousing 112, with the intermediate housing 118 separating the innerfiber bundle 120 and the outer fiber bundle 116, as discussed above.

The hollow fiber membranes of the outer fiber bundle 116 and the innerfiber bundle 120 are coupled to an upper potting 117 and a lower potting119 that are configured to fluidly communicate sweep gases into and fromthe hollow fiber membranes (e.g., into the hollow fiber membranes from agas inlet 121 and/or from the hollow fiber membranes to a gas outlet123, such as gas outlet 1 and gas outlet 2). Thus, the upper potting 117is positioned at an upper portion within the outer housing 112 and alower potting 119 is positioned at a bottom portion within the outerhousing 112. Furthermore, each of the inner fiber bundle 120 and theouter fiber bundle 116 are configured to be sealed from each other,including at the upper potting 117 and the lower potting 119, to preventundesired flow paths of the blood and/or sweep gases.

In one example, the sweep gas may be selected based on the clinicalapplication, such as by using oxygen or an oxygen-rich gas tosubstantially transfer oxygen to blood in the outer fiber bundle 116 andto substantially remove carbon dioxide in the inner fiber bundle 120.Alternatively, air (e.g., atmospheric air) or a combination of air andoxygen may be used. The flow of sweep gas is separated into flow paths(e.g., for transferring oxygen and for removing carbon dioxide) tocontrol the flow rate of each sweep gas and/or content independentlyfrom the other sweep gas.

Referring to FIGS. 1, 2, 5, 6, 14, 15, 17, 18, 20, 21 and 23, the dualchamber gas exchanger 100 is further configured to control how many ofthe hollow membrane fibers are in contact with the sweep gas. Forexample, one flow path can be controlled to independently deliver oxygenand/or air from another flow path. Thus, the dual chamber gas exchanger100 increases flexibility using various gas sources for oxygen transferand carbon dioxide removal. For example, depending on clinicalapplications, both of the inner fiber bundle 120 and outer fiber bundle116 can be used for oxygen transfer and/or carbon dioxide removal, oronly the outer fiber bundle 116 is used for oxygen transfer while theinner fiber bundle 120 is used to remove carbon dioxide and vice versa.

Furthermore, the dual chamber gas exchanger 100 can be configured toincrease the flow rate of one gas (e.g., oxygen or air). For example, asweep gas from one flow path can be recirculated such that it iscombined with the gas in the other flow path for a clinical applicationin which increasing oxygen may have a greater clinical need than carbondioxide removal. As a further example, the clinician can increase thesweep gas flow rate and/or surface area of the oxygenator membrane(further described below) that is exposed to air if increased carbondioxide removal is required.

Referring to FIGS. 2, 3, 6, 7, 14, 15, 17, 18, 20, 21, and 23, the firstchamber 110 of the dual chamber gas exchanger 100 can be configured totransfer the sweep gas (e.g., oxygen) to the blood or remove the carbondioxide from the blood. For example, the flow rate of the sweep gas fortransferring oxygen may be approximately between 1 liters per minute and6 liters per minute. An oxygen source then provides the sweep gas to thefirst chamber 110. In one embodiment, the oxygen source is a smallcapacity, light weight, battery operated, portable oxygen concentrator(e.g., a commercially-available oxygen concentrator).

The oxygen concentrator converts air into high oxygen concentration(e.g., approximately >90% oxygen concentration) gas. The oxygenconcentrator can be integrated into a portable drive console that isconfigured to enclose the oxygen concentrator and other components, suchas a power source (such as a battery), blood pump controls, flowsensors, and blood gas sensors (FIGS. 11 and 13). For example, oneembodiment can include a detachable pump 126 to form an integratedpump-oxygenator (e.g., integrated pump-oxygenator; see FIG.12) thatincludes a typical blood pump 126 and pump driver that are controlled bythe blood pump controls. The blood pump 126 can be simply coupled anduncoupled from the dual chamber gas exchanger 100 by using a quickconnector, typical fastener, or the like. However, in other embodiments,the oxygen source may be a fixed or portable oxygen tank, atmosphericair, or the like.

Again referring to FIGS. 2, 3, 6, 7, 14, 15, 17, 18, 20, 21, and 23, thesecond chamber 113 of the dual chamber gas exchanger 100 can beconfigured to remove carbon dioxide from the blood or transfer oxygen tothe blood. For example, the flow rate of the sweep gas for removingcarbon dioxide may be approximately 6 liters per minute to 18 liters perminute. In one embodiment, a small air fan compresses and mixes air withthe sweep gas (e.g., oxygen or oxygen-rich gas) from the first chamber110 to generate a high sweep gas flow for carbon dioxide removal. Theenclosed dual gas flow chamber 124 of the current embodiment ispositioned below the lower potting 119 or above the upper potting 117 ofthe inner fiber bundle 120 and the outer fiber bundle 116.

Still referring to FIGS. 2, 3, 6, 7, 14, 15, 17, 18, 20, 21, and 23, thedual gas flow chamber 124 includes the first chamber 110 and the secondchamber 113 that are each configured to receive one of the sweep gasesfrom the two gas inlets 121 (e.g., gas inlet 1 and gas inlet 2). Forexample, the sweep gases in each first chamber 110 and outer chamber 113may have different compositions and/or flow rates. The gas inlets 121distribute the sweep gases to the open lumen fibers that are imbedded inthe upper potting 117 and the lower potting 119 of the inner fiberbundle 120 and outer fiber bundle 116, respectively. In the currentembodiments, oxygen or oxygen-rich gas flows through open fiber lumensin the upper potting 119 and diffuses across an outer wall of individualhollow fiber membranes in the first chamber 110 into the blood whereblood oxygenation takes place. Furthermore, carbon dioxide from theblood diffuses into the lumens of the hollow fiber membranes and isremoved from the blood. The sweep gas flows through the hollow fibermembranes and exits the dual gas flow chamber 124 through the lowerpotting 119. In the current embodiments, the sweep gases exit the dualchamber gas exchanger 100 by venting into the atmosphere. Thus, the dualchamber gas exchanger 100 receives and diffuses the sweep gases intoseparate fiber membrane bundles for blood oxygenation and carbon dioxideremoval.

The outer housing 112 and intermediate housing 118 is configured to formindividual or mixed blood flow paths in the inner fiber bundle 120 andthe outer fiber bundles 116 (FIGS. 2, 3, 6, 7, 14, 15, 17, 18, 20, and21). In the current embodiments, various blood flow paths are possibleby opening and closing either or both blood flow gates 128 and 130 (seeFIGS. 2-4, 6-8B, 14-16, and 20-22). The blood flow gates are attached tothe outer housing 112, the intermediate housing 118, and the blooddistributor 114 that is coupled to a blood inlet 142. FIGS. 2-4 show anouter fiber bundle having a circumferential blood flow path (See arrowsin FIGS. 3 and 4). The blood distributor 114 receives blood from theblood inlet 142 and is fluidly coupled to a first rectangular blood gate128 (Gate 1) formed as a vertical slit or gap on one side of the outerhousing 112, and a second rectangular blood gate 130 (Gate 2) is locatedat the opposite side on the intermediate housing 118. In one embodiment,the blood distributor 114 substantially uniformly discharges throughGate 1 128 into the outer fiber bundle 116 in a substantiallycircumferential direction through the outer fiber bundle 116 and exitthrough Gate 2 130 into the intermediate annular space 132 (e.g., havinga cylindrical or conical-like shape) located between the inner wall ofthe intermediate housing 118 and the outer surface of the inner fiberbundle 120. As a further alternative, the dual chamber gas exchanger 100is configured to filter particulates in the blood. For example, the dualchamber gas exchanger 100 can include a filter, such as a depth filter,reticulated foam, microporous filtration, filtration mediums, or thelike.

In another embodiment of the dual chamber gas exchanger 100, shown inFIGS. 6-8B, the outer fiber bundle 116 has an axial blood flow path. Theblood distributor 114 is configured in the shape of a spiral-like volutehaving a cross-sectional area that is gradually decreasing (see e.g.,FIGS. 14-16, 17-19, and 20-22). FIGS. 5-8B illustrate that the blooddistributor 114 generally encircles a top end of the outer housing 112and attaches to the first blood gate 128 (Gate 1) that is generally likea thin slot. The second thin slot blood gate 130 (Gate 2) is located atan end of the intermediate housing 118 that is opposite to Gate 1 128.The spiral-like volute blood distributor 114 gradually discharges bloodcircumferentially (e.g., 360 degrees) into the top end of the outerfiber bundle 116 through Gate 1 128. Blood flows in the axial directionto exit the outer fiber bundle 116 and enter the intermediate annularspace 132 between the inner wall of the intermediate housing 118 and theouter surface of the inner fiber bundle 120 through Gate 2 130. The flowpath through the inner fiber bundle 120 is radial, which increasesbiocompatibility and gas exchange efficiency and has low pressure loss.

Still referring to FIGS. 6-8B, the intermediate annular space 132 isgenerally formed between the inner wall of the intermediate housing 118and the outer surface of the inner fiber bundle 120, and has a generallyuniform pressure distribution (e.g., prior to blood entering the innerfiber bundle 120). The blood has a generally uniform pressuredistribution that causes blood to flow in a substantially uniformradially inward direction through the fiber membranes of the inner fiberbundle 120 (see FIGS. 3, 4, 7, 8A and 8B, 18, and 19). Computationalfluid dynamics analysis demonstrates the substantially uniform flow andthe substantially uniform oxygen transfer in the inner fiber bundle 120and outer fiber bundle 116 (FIGS. 9A, 9B, 10A, and 10B).

Thus, the inner fiber bundle 120 and the outer fiber bundle 116 may beconfigured for various blood flow paths (e.g., circumferential, axial,and/or radial), depending on the clinical application. For example, oneembodiment of the dual chamber gas exchanger 100 includes the innerfiber bundle 120 having a radial flow path and the outer fiber bundle116 having a circumferential flow path (see FIGS. 2-4). As furtherexample, another embodiment of the dual chamber gas exchanger 100includes the inner fiber bundle 120 having a radial flow path and theouter fiber bundle 116 having an axial flow path (see FIGS. 6-8B). As astill further example, another embodiment of the dual chamber gasexchanger 100 includes the inner fiber bundle 120 having acircumferential flow path and the outer fiber bundle 116 having a radialflow path (see FIGS. 14-16). As a yet further example, anotherembodiment of the dual chamber gas exchanger 100 includes the innerfiber bundle 120 and the outer fiber bundle 116 having a radial flowpath (see FIGS. 17-19). As a further example, another embodiment of thedual chamber gas exchanger 100 includes the inner fiber bundle 120having an axial flow path and the outer fiber bundle 116 having a radialflow path (see FIGS. 20-22). Other combinations and configurations offlow paths are feasible within the dual chamber gas exchanger 100.

Referring to FIGS. 2, 3, 6, 7, 14, 15, 17, 18, 20, and 21, the innerfiber bundle 120 and the outer fiber bundle 116 of the currentembodiment are cylindrical annulus that include many hollow membranefibers, or microporous hollow fibers, e.g., having pore sizes that aregenerally less than 0.1 micron in diameter. The hollow membrane fibersof the current embodiment are commercially available and have an outerdiameter approximately between 250 microns and 400 microns, and a wallthickness approximately between 30 microns and 50 microns, althoughhollow fiber membranes having other outer diameters and wall thicknessesare feasible with the dual chamber gas exchanger 100. In anotherembodiment, the hollow membrane fibers are configured to beanti-thrombogenic, for example having an anti-thrombogenic coating(e.g., heparin or a functional equivalent). Alternatively, the hollowmembrane fibers may be microporous membranes to filter blood components,such as for blood dialysis.

The porosity (or void ratio) of each inner fiber bundle 120 and outerfiber bundle 116 is generally determined by the desired pressure lossacross the inner fiber bundle 120 and the outer fiber bundle 116. In thecurrent embodiment, the porosity ranges approximately between 0.4 and0.7. Alternatively, coated or skinned hollow fibers may be used topermit oxygen and carbon dioxide diffusion through a non-porous skinlayer of the outer wall of the membrane fibers. The hollow membranefibers are typically available commercially in a tape configurationwhereby individual hollow membrane fibers are arranged to apredetermined configuration (i.e. parallel straight or bias,multi-directional, woven, spaced, etc.) permitting tape wrapping to forma cylindrical or conical-like bundle configuration. Alternatively, thehollow fiber membranes can be wrapped or wound (e.g., like a spool ofkite-string). The hollow membrane fibers are attached to each of thelower potting 119 and upper potting 117 (see FIGS. 2, 3, 6, 7, 14, 15,17, 18, 20, and 21). For example, in the current embodiment, the ends ofthe inner fiber bundle 120 and the outer fiber bundle 116 are trimmed toopen inner lumens of the membrane fibers and cast-potted using a polymer(e.g., urethane, epoxy, or the like). The sweep gas is distributedthrough the inner lumens between the upper potting 117 and the lowerpotting 119.

In one embodiment, the dual chamber gas exchanger 100 includes a heatexchanger that is configured to control blood temperature. The heatexchanger may include a cylindrical annulus of heat exchange elementsaround at least one of the inner fiber bundle 120 or outer fiber bundle116. The cylindrical annulus is formed of a plurality of capillariesthat are potted to one of the inner fiber bundle 120 or the outer fiberbundle 116. The heat exchanger capillaries can be formed ofbiocompatible metals, polymers, or the like. The capillaries have lumensthat are opened to form a separated flow path. The heat exchangerfurther includes a sweep gas chamber and a heat transfer medium chamberthat are configured to control heat of the sweep gas and heat transfermedium, respectively. In the one embodiment, the sweep gas chamber andthe heat transfer medium chamber are disposed on top of the outerhousing 112 above the upper potting 117, however, in another embodimentthe sweep gas chamber and the heat transfer medium chamber are disposedbelow the outer housing 112 above the lower potting 119. The temperatureof the blood is controlled by varying a flow rate and temperature of theheat transfer medium as it flows through the heat exchanger capillariesand the hollow membrane fibers.

In an alternative embodiment, a plurality of hollow tubes are configuredfor heat transfer, rather than configuring the hollow fiber membranes asheat exchangers. Such a configuration uses a temperature-controlledfluid, such as water, to affect blood temperature change.

The gas inlet 121 (FIGS. 1-3 and 5-7) is configured to operate at a lowpressure while providing uniform sweep gas in the outer fiber bundle 116and/or the inner fiber bundle 120. The gas inlet 121 includes inflow andoutflow connectors that are sized to achieve desired blood flow ratesand pressures. For example, the dual chamber gas exchanger 100 caninclude typical ¼″ or ⅜″ barbed fittings that receive standarddevice-assisted extracorporeal circulation tubing.

One embodiment of the dual chamber gas exchanger includes an arterialsample port 136 and a venous sample port 138 (FIGS. 1 and 2) that areconfigured to permit operators to collect blood samples from the dualchamber gas exchanger 100 (e.g., using syringes, traditional stopcocks,obturator-type sample ports, and the like). The arterial sample port 136and the venous sample port 138 are further configured to allow anoperator to sample blood before the blood flows into the inner fiberbundle 120 and/or outer fiber bundle 116, and after the blood flowsexiting from the inner fiber bundle and 120/or outer fiber bundle 116 tocontrol various parameters (e.g., blood flow rates, gas transfer ratesand pH for the control of oxygen concentration).

In one embodiment, dual chamber gas exchanger 100 may be configured toremove air bubbles from the blood. One embodiment can include an outervent port 140 (FIGS. 1, 3, 5-7, 12-15, and 17) positioned near a portionof the dual chamber gas exchanger 100 where air bubbles generallyaccumulate. For example, the outer vent port 140 can be located at theouter wall of the outer housing 112 near the upper potting 117 (FIG.2).Furthermore, other embodiments of the dual chamber gas exchanger 100 mayinclude an inner vent port that is located near the top of theintermediate housing 118, such as the upper potting 117 of the innerfiber bundle 120 to remove air bubbles. Air bubbles typically resultfrom trapped air that is not adequately removed during priming, bybroken hollow membrane fibers, or from excessive negative pressureapplied to blood that forces gases out of solution.

As shown in FIGS. 23A and 23B, an oxygenator in accordance with theprinciples of the present invention may be configured with anoxygen-rich gas passing through one portion of a gas exchange fiberbundle and an air or other oxygen-depleted stripping gas passing throughanother portion of the fiber bundle. Optionally, such oxygenators mayhave gas flow paths in which an exhausted oxygen-rich sweep gas from oneof an inner fiber bundle or an outer fiber bundle mixes with atmosphericair for use as a sweep gas in the other of the inner fiber bundle orouter fiber bundle.

As shown in FIG. 23A, an exchanger 200 comprising a fiber bundle 210 isconfigured to reuse the oxygen-rich exhausted sweep gas from an innerfiber bundle 220 in an outer fiber bundle 216. For example, oxygen froman external source, such as a tank, or an oxygen concentrator isdiffused into the inner fiber bundle 220 through a lower portion orplenum 224 of the dual gas chamber. The oxygen-rich gas is partiallydepleted of oxygen as it passes through the inner fiber bundle 220 andthen passes through an upper plenum 228 where it is mixed withatmospheric air entering through inlet 230. The combined gas flows thenpass down the outer fiber bundle 216 to remove or “strip” carbon dioxidefrom the blood entering the fiber bundle 210 horizontally in any of theflow paths previously described. The combined gases, although not oxygenrich, will nonetheless provide an initial stage of oxygenation inaddition to stripping the carbon dioxide. Oxygenation is completed inthe inner fiber bundle 220 where the blood is exposed to a gas having ahigher oxygen concentration. The sweep gas is ventilated into theatmosphere from a bottom portion of the dual gas chamber 232. Thus, thegas flow rate and oxygen utilization efficiency for mixed atmosphericand oxygen sweep gas can be increased because atmospheric air isgenerally abundant and simple to use in the dual chamber gas exchanger200.

Referring to FIG. 23B, an alternative embodiment of a dual chamber gasexchanger embodiment 250 may be configured to pass an oxygen-rich sweepgas 252 through an inner fiber bundle 260 only and only pass atmosphericair 254 through an outer fiber bundle 262 only. The arrangement ofplenums and isolation barriers will be made accordingly.

In FIG. 24, an oxygenator 300 has a rectangular shape with separate gasinlets 323 and 324 at the top and a rectangular fiber bundle 302 placedbetween an upper potting 317 and a lower potting 319. In contrast toprevious embodiments, the fiber bundle 302 is free from barriers thatcreate isolated air flow regions therein. Gas flow through the fiberbundle 302 is controlled by a moveable partition 304 which is positionedin a gas inlet region 306 above the upper potting 317. The gas inlets323 and 324 release gas on opposite sides of the partition 304 and maybe connected to different gas sources, such as air and oxygenrespectively. Moving the partition 304 will thus adjust the fiber areasto which each gas is exposed. For example, blood flowing in thedirection of the horizontal arrow in FIG. 24 would first be exposed tothe gas entering through inlet 323, which could be an air or other lowoxygen stripping gas. After carbon dioxide is at least partiallystripped, the blood could be exposed to an oxygen rich gas deliveredthrough inlet 324 for complete oxygenation. Blood of course is flowingvertically in the direction of the vertical arrows. In some embodiments,the partition 304 could be fixed. While adjustability of the fiber areaswould be lost, the efficiency of stripping carbon dioxide from the bloodusing air or other low oxygen gas and achieving final oxygenation withpure or other high oxygen gas would be retained.

In a further embodiment, as illustrated in FIG. 25, an oxygenator 400has a cylindrical shape with separate gas inlets 423 and 424 at the topand an annular fiber bundle 402 placed between an upper potting and alower potting (not shown). A circular partition 404 having an adjustablediameter is positioned in a gas inlet region 406 above the upperpotting. The gas inlets 423 and 424 will be positioned to lie outside ofand inside of the partition 406 and may be connected to different gassources, such as air and oxygen respectively. Adjusting the diameter ofthe partition 404 will adjust the fiber areas to which each gas isexposed. For example, blood flowing in the direction of the horizontalarrow in FIG. 24 would first be exposed to the gas entering throughinlet 423, which could be an air or other low oxygen stripping gas.After carbon dioxide is at least partially stripped, the blood could beexposed to an oxygen rich gas delivered through inlet 424 for completeoxygenation. Blood of course is flowing vertically in the direction ofthe vertical arrows. In some embodiments, the partition 404 could befixed. While adjustability of the fiber areas would be lost, theefficiency of stripping carbon dioxide from the blood using air or otherlow oxygen gas and achieving final oxygenation with pure or other highoxygen gas would be retained.

In yet another embodiment of the present invention, shown in FIGS. 26Aand 26B, a dual chamber gas exchanger 500 (similar to the dual chambergas exchangers 100 as described above) is further configured to varysweep gas exchange rates independently of the sweep gas concentrations(e.g., without varying the flow rates and/or concentration of the sweepgases). The dual chamber gas exchanger 500 includes a partitionmechanism 510, which in one embodiment is an adjustable aperture such asan iris mechanism that is configured to vary a portion of the surfacearea of the dual chamber gas exchanger membrane 512 that is in contactwith blood for transferring oxygen and also to vary a portion of thesurface area of the dual chamber gas exchanger membrane 512 that is incontact with blood for carbon dioxide removal, as described above.

The partition mechanism 510 varies the portions of sweep gases for gasexchange by varying access or fluid communication of the sweep gasesinto separate paths through different regions within the fiber bundlewithout a physical chamber wall (e.g., intermediate housing). Varyingaccess by controlling and adjusting the areas of the gas flow paths(e.g., portion of the hollow fiber membrane exposed to the inlet gasflow) in which the sweep gases are exposed to a patient's blood flowallows a clinician to more accurately and efficiently match thepatients' requirements (e.g., metabolic needs).

In the illustrated embodiment, the partition mechanism 510 is amechanical mechanism (FIG.26B), such as an iris-type or shutter-typemechanism that is configured to vary an opening area to control the flowgas. In other embodiments, the opening area may have a circular orhexagonal-like shape, such that the opening area is varied by varying adiameter or width. The partition mechanism 510 is fluidly coupled withat least one of the upper potting 514, lower potting 516. A spiralvolute may distribute the gas to the fiber bundle (FIG. 26B) oralternatively, a vrticluscal inlet (as provided in prior embodiments)may be used (FIG. 26A). The partition mechanism 510 can be a valve orplurality of valves, such as an array or series of valves that controlsfluid access to various flow paths, such as described above. The openingarea of the partition mechanism 510 is controlled by a controller, suchas by the blood pump controls described above. The partition mechanism510 thus allows the dual chamber gas exchanger 500 to control themixture and rate of sweep gases into portions of the dual chamber gasexchanger membrane 512 exposed to and in fluid contact with thepatients' blood to transfer oxygen and to remove carbon dioxide.

The present invention is a dual chamber gas exchanger device. The dualchamber gas exchanger is configured to increase the efficiency of gasexchange, such as with oxygen and carbon dioxide, relatively lowpressure loss, good biocompatibility, and unique flexibility but requireminimal volume and blood contacting surface. The dual chamber gasexchanger increases options for optimal blood flow paths and efficiencyof gas transfer in an inner fiber bundle and an outer fiber bundle. Thedual chamber gas exchanger also reduces the amount of oxygen requiredfor oxygen transfer to the blood and carbon dioxide removal from theblood simultaneously. The reduced oxygen requirements and reduced sizeand weight of the dual chamber gas exchanger device further increasesthe variety of applications of use. For example, the dual chamber gasexchanger can operate with a small portable oxygen concentrator havinglow power consumption to provide a sweep gas for oxygen transfer andcarbon dioxide removal that is required in ambulatory uses and the like.

Additionally, the dual chamber gas exchanger is further configured toenhance gas exchange using an active mixing mechanism. The active mixingmechanism uses an inner fiber bundle and an outer fiber bundle todecrease the boundary layer effect of blood flow and improve gasexchange efficiency. The intermediate housing and the inner fiber bundleform a cylindrical or conical-like space that is configured to increasethe interaction of blood with membranes by enabling high momentum bloodflow in the space between the membrane outer surface and inner housingwall, such that blood encounters lower flow resistance, increasedturbulence, and increased mixing after passing through the outer fiberand before entering the inner fiber bundle. Thus, the dual chamber gasexchanger mixes the blood without introducing unnecessary high shearrates or stagnant zones as in typical blood oxygenating devices.Moreover, the dual chamber gas exchanger includes fewer components thantypical blood oxygenating devices. The dual chamber gas exchanger isconfigured to increase maintainability and operability, compared totypical blood oxygenating devices, by increasing access to joints andbonding area.

While the above is a complete description of the preferred embodimentsof the invention, various alternatives, modifications, and equivalentsmay be used. Therefore, the above description should not be taken aslimiting the scope of the invention which is defined by the appendedclaims.

What is claimed is:
 1. A blood oxygenator comprising: a housingcomprising a blood inlet, a blood outlet, a stripping gas inlet, and atleast one gas outlet; and an oxygenator fiber bundle disposed within thehousing, the oxygenator fiber bundle having a stripping region receivingstripping gas from the stripping gas inlet, and the oxygenator fiberbundle further having an oxygenation region receiving oxygenation gasfrom the oxygenation gas inlet.
 2. The blood oxygenator of claim 1,wherein the fiber bundle is cylindrical and at least a portion of theblood flow path is at least one of (i) radially inward or radiallyoutward, (ii) annular, and (iii) unidirectional across the oxygenatorfiber bundle.
 3. The blood oxygenator of claim 1, wherein the fiberbundle is cylindrical and an outer portion of the blood flow pathfollows an annular path and an inner portion follows a radially inwardpath.
 4. The blood oxygenator of claim 3, wherein the blood inlet feedsthe outer portion and the inner portion feeds the blood outlet.
 5. Theblood oxygenator of claim 4, wherein the stripping region is disposed atleast in part in the outer portion of the blood flow path and theoxygenation region is disposed at least in part in the inner portion ofthe blood flow path.
 6. The blood oxygenator of claim 3, wherein theblood inlet feeds the inner portion and the outer portion feeds theblood outlet.
 7. The blood oxygenator of claim 6, wherein the strippingregion is disposed at least in part in the inner portion of the bloodflow path and the oxygenation region is disposed at least in part in theouter portion of the blood flow path.
 8. The blood oxygenator of claim3, further comprising a cylindrical wall separating the outer portionand the inner portion of the cylindrical fiber bundle, wherein bloodflows from the blood inlet through an axial opening in the housing intothe outer portion of the fiber bundle and flows annularly through theouter portion of the fiber bundle to and through an axial opening in thecylindrical wall into a distribution ring surrounding the inner bundlefrom where the blood flows radially inwardly through the inner portionof the fiber bundle to an axial collection region along a center axis ofthe inner portion of the fiber bundle.
 9. The blood oxygenator of claim1, wherein the oxygenation fiber bundle has a cross-sectional area andthe stripping region that receives the stripping gas from the strippinggas inlet has an inlet area that comprises from 20% to 80% of thecross-sectional area and the oxygenation region that receives theoxygenation gas from the oxygenation gas inlet has an inlet area thatcomprises from 80% to 20% of the cross-sectional area.
 10. The bloodoxygenator of claim 9, further comprising a manifold divider whichdirects the stripping gas from the stripping gas inlet to the strippingregion of the oxygenator fiber bundle and directs the oxygenation gasfrom the oxygenation gas inlet to the oxygenation region of theoxygenator fiber bundle.
 11. The blood oxygenator of claim 10, whereinthe manifold divider is disposed in a manifold which receives thestripping gas from the stripping gas inlet and the oxygenation gas fromthe oxygenation gas inlet, wherein the manifold is open to an entire gasinlet side of the oxygenation fiber bundle and placement of the manifolddivider controls an inlet area of the stripping region that receives thestripping gas from the stripping gas inlet and an inlet area of theoxygenation region that receives the oxygenation gas from theoxygenation gas inlet.
 12. The blood oxygenator of claim 11, wherein themanifold divider is moveable.
 13. The blood oxygenator of claim 11,wherein the manifold divider is fixed.
 14. The blood oxygenator of claim1, wherein the oxygenation fiber bundle further comprises an upperpotting and a lower potting, wherein the manifold is located within thehousing adjacent to one of the pottings.
 15. The blood oxygenator ofclaim 1, further comprising a blood pump connected to said blood inlet,an oxygenation gas source connected to the oxygenation gas inlet and astripping gas source connected to the stripping gas inlet.
 16. A methodfor oxygenating blood comprising: providing a blood oxygenator having(1) a housing with a blood inlet, a blood outlet, a stripping gas inlet,an oxygenation gas inlet, and at least one gas outlet and (2) anoxygenator fiber bundle disposed within the housing; flowing bloodthrough the blood inlet, through the oxygenator fiber bundle, and outthrough the blood outlet; and flowing a stripping gas through thestripping gas inlet and an oxygenation gas through the oxygenation gasinlet, wherein the stripping gas flows through a stripping region of theoxygenator fiber bundle and the oxygenation gas through an oxygenationregion of the oxygenator fiber bundle; wherein the stripping gas regionof the oxygenator fiber bundle is upstream of the oxygenation region ofthe oxygenator fiber bundle.
 17. The method of claim 16, wherein theblood travels through the stripping region of the oxygenator fiberbundle in an annular flow path.
 18. The method of claim 16, wherein theblood travels through the oxygenation region of the oxygenator fiberbundle in a radially inward flow path.
 19. The method of claim 16,wherein the blood travels through the stripping region and theoxygenation region of the oxygenator fiber bundle in a straightdirection.
 20. The method of claim 16, wherein the blood travels throughthe oxygenator fiber bundle in a substantially uniform blood flowdistribution.
 21. The method of claim 16, wherein the fiber bundle has across-sectional area and the stripping region that receives thestripping gas from the stripping gas inlet has an inlet area thatcomprises from 20% to 80% of the cross-sectional area and theoxygenation region that receives the oxygenation gas from theoxygenation gas inlet has an inlet area that comprises from 80% to 20%of the cross-sectional area.
 22. The method of claim 21, furthercomprising moving a manifold divider which directs the stripping gasfrom the stripping gas inlet to the stripping region of the oxygenatorfiber bundle and directs the oxygenation gas from the oxygenation gasinlet to the oxygenation region of the oxygenator fiber bundle to adjustrelative areas of the stripping region and the oxygenation region of theoxygenation fiber bundle.